Electrical cables are used in conjunction with a printed wiring board (PWB) to conduct electrical signals between a location on the PWB and another location in the circuit. Such electrical cables typically include a center conductor surrounded by a dielectric or insulating layer. In a coaxial cable, the cable also includes a shield layer surrounding but electrically isolated from the center conductor.
In modern electronic devices, surface mount techniques are used to minimize the area required for mounting of components such as electrical cables. Components and cable terminations are soldered directly to the surface of the PWB, eliminating the space and expense required for plated-through solder holes. Also, surface mounted components may be placed automatically by a pick and place machine, reducing cost and time for manufacture and improving quality.
Previously, surface mount assembly of cables has been labor-intensive and prone to rejection for poor quality. At the manufacturer, cables are cut to size and the center conductor is formed by bending the center conductor at one or both ends. Forming is required for two purposes. The center conductor is bent in a direction from the center axis toward the edge of the jacket to provide planarity between the soldered portion of the center conductor and the jacket. The center conductor is also bent in a direction parallel to the surface of the PWB to minimize rolling of the cable during mounting to the surface. Rolling occurs using un-bent cables because the cable is round in cross section and the cable is soldered to surface mount pads rather than plated through holes. Cables are bent in specified orientations to reduce the effect of rolling and provide planarity.
Cables handled in this manner are often rejected as not meeting quality control requirements. Many such cables are extremely thin. The center conductor is as small as 0.002-0.003 inches. In the process of forming the end and subsequently handling the cable, the center conductor may be damaged or broken. The required coplanarity of the center conductor and the jacket may be disturbed. Any of these may cause the cable assembly to be rejected.
One previous apparatus for attaching coaxial cables to a PWB surface requires two separate connectors. One connector attaches to the PWB and the other attaches to the cable. The two connectors are then joined at the time of assembly. Use of two separate connectors increases the expense and labor of assembly, requires additional time for assembly and creates another failure mechanism, as the two connectors may not make adequate connection. This previous apparatus has not been a satisfactory solution to the surface mount problem.
Accordingly, there is a need in the art for an improved surface mount termination for coaxial and other cables.